Problem: Simplify the following expression: $\sqrt{99} - \sqrt{11}$
First, try to factor any perfect squares out of the radicals. $= \sqrt{99} - \sqrt{11}$ $= \sqrt{9 \cdot 11} - \sqrt{11}$ Separate the radicals and simplify. $= \sqrt{9} \cdot \sqrt{11} - \sqrt{11}$ $= 3\sqrt{11} - \sqrt{11}$ Finally, simplify by combining the terms. $= ( 3 - 1 )\sqrt{11} = 2\sqrt{11}$